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- INFO-HAMS Digest Thu, 21 Dec 89 Volume 89 : Issue 1055
-
- Today's Topics:
- ARRL NR 91: HF DATA FILING
- pudgy wound helical antenna (60m vertical in my living room!)
- QST misinformation...
- W1AW: Computer-generated QRM ?
- ----------------------------------------------------------------------
-
- Date: 21 Dec 89 05:00:47 GMT
- From: samsung!cs.utexas.edu!asuvax!stjhmc!f1.n234.z1.fidonet.org!Jim.Grubs@zaphod.mps.ohio-state.edu,
- Subject: ARRL NR 91: HF DATA FILING
- Message-ID: <9960.2590EF49@stjhmc.fidonet.org>
-
- > Message-ID: <1385@n8emr.UUCP>
- >
- > ARRL BULLETIN 91 (ARLB091) 12/15/89
- >
- > ON DECEMBER 12, ARRL COUNSEL CHRIS IMTAY, N3AKD, FILED A PETITION
- > FOR RULE MAKING WITH FCC SEEKING THE ADOPTION OF RULES TO PERMIT
- > LIMITED HF RTTY AND DATA COMMUNICATION UNDER AUTOMATIC CONTROL.
-
- Bravo!! Thanks for the good news.
-
- 73 de W8GRT
-
-
-
- --
- Uucp: ...{gatech,ames,rutgers}!ncar!asuvax!stjhmc!234!1!Jim.Grubs,.W8GRT
- Internet: Jim.Grubs,.W8GRT@f1.n234.z1.fidonet.org
-
- ------------------------------
-
- Date: 22 Dec 89 01:38:29 GMT
- From: ems@apple.com (Mike Smith)
- Subject: pudgy wound helical antenna (60m vertical in my living room!)
- Message-ID: <5937@internal.Apple.COM>
-
- In article <1260015@hpmwtlb.HP.COM> timb@hpmwtd.HP.COM (Tim Bagwell) writes:
- >> Yes it is possible to resonate out the capacitive reactance of the short antenna
- >> by a lumped or distributed inductance but what you end up with is usually a
- >> very small radiation resistance! This means that the ratio of radiation
- >> resistance to "ohmic" resistance drops and you loose your power to heat.
- >> In ship board MF antennas the radiation resistance is often less than a on
- >> ohm! (Moral of the story: Use thick wire or tube for short antennas!)
- >
- >True and another reason why a small diameter helical antenna is worse than
- >a simple vertical of comparable height and wire size.
-
- Ah, but by how much is it worse?
-
- Ummm, but I'm not transmitting. Im, well, umm, one of those SWL folks
- who like to listen .... Since efficiency isn't as important as SN ratio
- for a reciever why do I care? Yeah, I will have a little less signal,
- but that isn't nearly as much of a problem as finding a place to put
- up a 31 meter (or 60 meter!) vertical ...
-
- Per _The ARRL Antenna Book_ page 6-18 heading 'Short Helically Wound
- Vertical Antennas'
-
- Shortened quarter-wavelength vertical antennas can be made by
- forming a helix on a long cylindrical insulator. The diameter
- of the helix must be very small in terms of wavelength in order
- to prevent the antenna from radiating in the the axial mode.
- Acceptable form diameters for HF-band operations are from 1 inch
- to 10 inches when the practical aspects of antenna construction
- are considered.
-
- Looks to me like 4" diameter is in the reasonable range. The diameter
- should be small in terms of wavelength, so I would expect that for
- a 31 meter band antenna even using a 1 meter diameter would be OK;
- though with some increased tendency for 'high angle radiation' as
- the mode of radiation starts to shift from broadside to axial.
- Though it does say 'very small' so maybe 1/30th isn't very small...
-
- And further on:
-
- No strict rule has been established concerning how short a
- helically wound vertical can be before a significant drop in
- performance is experienced. As a general recommendation, one
- should use the greatest amount of length consistent with
- available space. A guideline might be to maintain an element
- length of 0.05 wavelength or more for antennas which are
- electrically a quarter wavelength long. Thus, use 13 feet or
- more of stock for an 80-meter antenna, 7 feet for 40 meters,
- and so on.
-
- This works out to 5 feet for a 31 meter antenna, so a 4 foot length
- should still be OK unless there is some profound non-linearity that
- isn't mentioned... Though I must admit that adding a loading coil to
- it for use on 60 meters was clearly a bit of whimsey and would be
- subject to loading coil losses. (But it was fun, though!)
-
- and:
-
- No specific rule exists concerning the size or type of wire one
- should use in making a helix. Larger wire sizes are, or course,
- preferable in the interest of minimizing I**2R losses in the
- system. For power levels up to 1000 watts it is wise to use
- a wire size of of no. 16 or larger.
-
- Since I'm using it as a recieving antenna I don't have much 'I' to
- square and I would expect that no. 16 wire would be serious overkill.
- It doesn't look like copper tubing is needed.
-
- They then go on to discuss the use of an L network to match the low
- impedance (which they say is on the order of 5 ohms - I still need to
- figure out how to properly measure mine with the antenna bridge...) and
- show a practical antenna design for 7 MHz with 2:1 SWR over 50 kHz.
- (NOT pudgy wound though...).
-
- (There is also the mention of using helically wound ground plane
- elements for the counterpoise, but that is another discussion)
-
- In summary, I don't contest your observations; they are quite true.
- The numbers need to be looked at to see if they are important.
-
- I think that the above quotes are evidence that, with a matching
- network, the effects you describe are not significant for an antenna
- used for recieving the 31 meter band that is 4 feet long and 4" in
- diameter; and are probably not important for transmitting if no. 16
- or larger wire were used.
-
- What do you think? Have I missed something in my interpretation of
- what they have presented as fact? Are their rules of thumb off base?
-
-
- --
-
- E. Michael Smith ems@apple.COM
-
- 'Whatever you can do, or dream you can, begin it. Boldness has
- genius, power and magic in it.' - Goethe
-
- I am not responsible nor is anyone else. Everything is disclaimed.
-
- ------------------------------
-
- Date: 21 Dec 89 14:43:44 GMT
- From: zaphod.mps.ohio-state.edu!usc!cs.utexas.edu!asuvax!stjhmc!f670.n142.z1.fidonet.org!Luck.Hurder@tut.cis.ohio-state.edu (Luck Hurder)
- Subject: QST misinformation...
- Message-ID: <9961.2590EF50@stjhmc.fidonet.org>
-
- All de KY1T:
-
- There's a bit of misinformation going around that I'd
- like to set straight, folks. A USENET user (?), perhaps
- N8DGN, I can't be sure, has been saying the following here
- on the echo:
-
- > They (the ARRL) are now changing their tune where microwave
- > coverage in QST is concerned. It is not acceptable to
- > ENTIRELY DROP microwave coverage from QST as they have
- > done.
-
- QST has done no such thing. They have merely dropped one column.
- They fully intend to continue publishing any and all acceptable
- articles regarding microwave that come their way.
-
- > I wasn't asking for the ARRL to increase their microwave
- > coverage, just to include some in QST
-
- Which is precisely what they are doing...
- > Paul Rinaldo, who is the editor of QST, made the decision
- > to CUT ALL microwave coverage
-
- False. Wrong. Uh-uh, no way. This guy isn't reading the letter
- that Paul wrote very well...
-
- > I cannot accept his decision to TOTALLY CUT
- > ALL microwave coverage.
-
- Hey, I wouldn't accept that either, if I were an ARRL member,
- which I am. Fact is, no such decision was made.
-
- Once again - QST will publish articles that relate to microwave
- activity as they always have done, provided that the articles
- make it through the article-review process that all authors
- must endure, and provided that the articles meet the normal
- standards. Those standards, by the way, appear
- in the January issue of QST for all to see. No secrets here,
- simply normal, every-day public knowledge..
- To put things in a different light for a second, I could squack
- up a storm too, if I so chose. The same financial dilemma that
- forced the microwave column to go that-a-way was also responsible
- for my Public Service column to be cut by a whole page every
- month. Public Service, traffic handling, and such were -- by
- the way -- the things that the ARRL were FOUNDED on. If I
- were to run around screaming that QST had dropped coverage
- of public service activities, I'd be laughted out of the office!
- Particularly with a FIVE pager coming up in the February issue
- relating to the public service efforts of the many hundreds
- of amateurs during the aftermath of Hurricane Hugo.
-
- Enough soapbox. 73 de KY1T
-
-
-
-
- --
- Uucp: ...{gatech,ames,rutgers}!ncar!asuvax!stjhmc!142!670!Luck.Hurder
- Internet: Luck.Hurder@f670.n142.z1.fidonet.org
-
- ------------------------------
-
- Date: 21 Dec 89 23:01:29 GMT
- From: hpl-opus!hpnmdla!alanb@hplabs.hp.com (Alan Bloom)
- Subject: W1AW: Computer-generated QRM ?
- Message-ID: <1250103@hpnmdla.HP.COM>
-
- Perry Scott asked why W1W doesn't listen before they transmit bulletins
- and code practice. I was a W1AW operator many years ago, so perhaps I can
- reply.
-
- The problem is that they transmit on all ham bands 160 thru 2 meters
- simultaneously. It would take an army of operators to listen to each
- frequency before each transmission. They switch between CW RTTY and
- phone frequencies dozens of times each day to maintain the published
- schedule, so you can see the impracticality of listening on each freq.
-
- The other problem is what to do if the frequency is in use. If the users
- refuse to move, you either have to transmit on top of them (which could
- be construed as intentional interference, a violation of the rules) or
- try to change frequency. The latter option would make it difficult for
- W1AW's listeners to find the station when needed.
-
- The times and frequencies are published in advance. I realize not too
- many of us have the W1AW schedule memorized, but many/most CW operators
- are aware of the W1AW frequencies and try to avoid them. On phone, the
- bulletins only take a few minutes to send, so the interference is
- minimized. I am of the opinion that not too many people listen to W1AW
- bulletins on phone anyway, so ARRL should just eliminate them.
-
- Al N1AL
-
- ------------------------------
-
- End of INFO-HAMS Digest V89 Issue #1055
- ***************************************
-
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